Carrier-wave generating system



April 16, 1946. CASE 2,398,694

CARRIER-WAVE GENERATING SYSTEM Filed March 20 1942 3 Sheets-Sheet 5NELSON P. CASE ATTORNEY Patented Apr. 16, 1946 2,888,894 CARRIER-WAVEGENERATING SYSTEM Nelson P. Case, Great Neck. N.

Hueltlne Y assignmto rporatlon, a corporation 0! Delaware ApplicationMai-en so. 1942, semi! No. 435.441 19 Claims. (Oletc-so) The presentinvention relates to carrier-wave generating systems and, particularly,to such systems adapted to generate a carrier wave having any selectableone of a number of predetermined constant frequencies in a predeterminedfrequency band, each such frequency corresponding to a desiredtransmission channel.

It is frequently desirable to provide a highirequency carrier-wavegenerating system capable of generating a carrier wave having a constantor stabilized frequency on any selectable one of a predetermined numberof transmission channels located in a predetermined high-frequency band.Such systems have many useful applications. For example, in the field ofmarine communication, a predetermined number of transmission channelsare allocated for use in ship-to-shore communication in the vicinity ofa given port and, since the number of ships in that locality desiring touse such channels may exceed the number of channels assigned to suchservice, it would be undesirable to assign a particular channel to agiven ship. A person having available the carrier-wave generating systemof the type described can listen on the air to find a channel which isnot used at that moment and may then quickly and readily set histransmitting apparatus for operation on a non-used channel.

There are only a limited number of radio transmission channels availablein the portion oi the frequency spectrum normally used at the presentday. The demands upon the available channels necessitate thatinterchannel interference he reduced to a minimum by the use orcarrier-wave generating systems having a high degree of frequencystability. Piezoelectric crystals are con ventionally used for thispurpose. Where the carrier-wave generating system must operate on anyselectable one of a number of pro-determined transmission channels, theproblem arises as how best to stabilize the frequency of the system oneach of these channels. Individual crystals may, of course, be providedfor each such channel. This has the disadvantage, however, that itrequires a large number of relatively expensive crystals and requires acomplicated switching arrangement by which the crystals are selectivelyincluded in circuit with the oscillator of the gen. erating system.

In one arrangement of the prior art it has been proposed thatmultihannel transmission be pro-- vided by the use of a relativelyhigh-frequency carrier-wave generator, a tunable low-frequencyoscillator which is relatively stable in absolute frequency by virtue ofthe fact that it generates only low frequencies, a modulator by whichthe high-frequency carrier wave is modulated with the low-frequencygenerated oscillations to provide a modulated-carrier wave including acarrler-wave component and modulation sideband components, and aselector for selecting one sideband of the modulated-carrier wave toderive a modulation component which is used as the carrier wave forradiation. This prior art arrangement has several disadvantages. Noprovision is made for precisely tuning the generating system to definitepredetermined transmission channels, this being done only by the methodof manually tuning the low-frequency oscillator as closely as manualmanipulation will permit to any desired channel. There is the furtherdisadvantage that the system is capable of operating only over a verylimited operating-frequency band. Additionally, there is thedisadvantage that the selector which selects the desired sidebandcomponent of the modulated-carrier wave generally cannot, in practice,he designed to select only the desired component to the exclusion of thecarrierwave component and the other modulation sideband component, withthe result that the latter components are apt to be radiated asundesired spurious carrier waves which may create undesired interferenceon other transmission channels.

In accordance with another prior art arrangement, it has been proposedthat precise multiplechannel operation of a carrier-wave generator ondefinite selected transmission channels be provided by the use of alow-frequency crystal-controlled osclllator having a frequency equal tothe frequency separation of desired transmission channels. There isderived from this oscillator a modulation signal having frequencieswhich are harmonically related to the frequency of the lowfrequencyoscillator. A high-frequency crystalcontrolled oscillator generates acarrier wave which is modulated with the modulation signal to derive acarrier wave having modulation sideband components which define desiredequally-spaced transmission channels. A selected component of themodulated-carrier wave is used as the carrier wave which is radiated.While this prior art arrangement is adapted to operate over a wide bandof operating frequencies, it is subject, as in the arrangementpreviously described, to the radiation of undesired modulationcomponents as undesired spurious carrier waves. The radiation of suchspurious carrier waves causes, of course, undesired interference withcommunications on channels other than that which, at any given time, isused by the carrier-wave generating system described.

It is an object of the present invention, therefore, to provide a newand improved carrier-wave generating system which avoids one or more ofthe disadvantages and limitations of the prior art systems.

It is a further object of the invention to provide an improvedcarrier-wave generating system in which a single frequency standard iseffective to maintain the frequency of a relatively highfrequencycarrier wave substantially constant on any selectable transmissionchannel in a wide band of such channels.

It is an additional object of the invention to provide a carrier-wavegenerating system adapted to generate a relatively high-frequencycarrier wave and in which the frequency of the wave generated ismanually adjusted app y 130 that suitable for operation of the system onany selected transmission channel in a wide band of such channels andthe generator-is thereafter automatically controlled to adjust it moreaccurately to and maintain it on such selected channel.

It is a further object of the invention to provide a carrier-wavegenerating system in which a plurality of frequency standards areeffective to establish and maintain the frequency of a relativelyhigh-frequency carrier wave substantially constant on any selectabletransmission channel in one of a plurality of wide bands of suchchannels after the frequency of the carrier wave has been manuallyadjusted approximately to the frequency corresponding to such selectedchannel, each of such bands of channels being defined by a particularone of the frequency standards and the transmission channels of one bandintervening between the channels of at least a portion of one or more ofthe others of the bands.

In accordance with the invention, a carrierwave generating systemcomprises means for generating a. carrier wave including a carrier-wavecomponent of relatively high and substantially constant frequency andsideband components of substantially constant frequency and extendingover a predetermined frequency band. The system includes means forgenerating a second wave having any selectable frequency in apredetermined band equal to but displaced by a predetermined value inthe frequency spectrum from the first-mentioned frequency band. There isalso included in the system means responsive Jointly to the frequency ofthe second wave and the frequency of that one of the aforesaidcomponents of the first wave which is displaced in the frequencyspectrum by a predetermined value from the desired operating frequencyof the second wave for maintaining the frequency of the second wave at asubstantially constant desired value.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a schematic circuit diagram ofa complete carrier-wave generating system embodying the presentinvention; Fig. 2 is a frequency scale used as an aid in explaining theoperation of the Fig. 1 arrangement; Fig. 3 is a schematic circuitdiagram of a complete carrier-wave generator embodying a modified formof the invention; and Figs. 4 and 5 are frequency scales used inexplaining alternative modes of mention of the Fig. 3 arrangement.

Referring now more particularly to Fig. 1 of the drawings, there isrepresented schematically a complete carrier-wave generating systemembodying the present invention in a particular form. The systemincludes means for generating a carrier wave of high and substantiallyconstant frequency comprising an oscillator Hi, this means includingmeans for maintaining the frequency thereof substantially constantcomprising, preferably, a piezo-electric crystal l I. The system alsoincludes means for generating a modulation signal having frequencycomponents of substantially constant frequencies and predeterminedfrequency spacing relative to each other. preferably a frequency spacingequal to that between equally-spaced desired transmission channels,comprising an oscillator I2 and a harmonic generator is having an inputcircuit coupled to the output circuit of the oscillator i2. Since thefrequency components of the modulation signal derived by the harmonicgenerator l3 are harmonically related, it will be seen that they haveequal frequency spacings relative to each other and, as will becomeapparent hereinafter, define equally-spaced predetermined desiredtransmission channels. The system additionally includes means formodulating the carrier wave generated by oscillator lfl with themodulation signal generated by units l2 and I3 to derive a carrier waveincluding a carrier-wave component of relatively high and constantfrequency and sideband components of substantially constant frequenciesand extending over a predetermined frequency band. This last-named meanscomprises a modulator if having one input circuit coupled to the outputcircuit of harmonic generator 13 and another in put circuit coupled tothe output circuit of oscillator Ill and havin an output circuit inwhich is developed the aforementioned carrier wave including thecarrier-wave component and sideband components.

The carrier-wave generating system of the invention also includes meansfor generating a second wave having any selectable frequency in apredetermined frequency band equal to but displaced in the frequencyspectrum from the fre quency band of the above-mentioned modulatedcarrier wave, hereinafter referred to as the control carrier wave forsimplicity, developed by units I044, inclusive. This means comprises anoscillator l5 having an adjustable tuning element comprising a condenserl6 for tuning the oscillator l5 approximately to a desired operatingfrequency. Since in practice it is desirable for numerous reasons, suchas lower cost, the increased ease of making, and increased ruggedness,that the piezoelectric crystal ii have a frequency as low as thecircumstances permit, the frequency band of the oscillator l5 preferablylies above the frequency band of the control carrier wave. I

There is also included in the carrier-wave generating system meansresponsive jointly to the frequency of the second wave, which isgenerated by the oscillator l5, and the frequency of that one of thefrequency components of the control carrier wave which is displaced inthe frequency spectrum by a predetermined selectable value from thecarrier-wave component of the latter wave for maintaining the frequencyof the second wave at a substantially constant desired value. Thislast-named means comprises a modulator if having a first input circuitcoupled aaaacoc to the output circuit of modulator It and a second inputcircuit coupled to the output circuit of oscillator II, the modulator ilhaving an output circuit coupled to an intermediate-frequency amplifierll of one or more stages. There is coupled to the output circuit ofamplifier it, in the order named, a frequency detector l9 and afrequency shifter 20, which may comprise a reactor tube, coupled acrossa frequency-control circuit of oscillator II. The output circuit ofoscillator I! is coupled to the input circuit of a unit II which mayinclude an amplitude-modulator stage and a tunable radio-frequencyamplifier of one or more stages. The modulation signal to be transmittedis applied to the modulator of unit 21 in conventional manner. Theoutput of the radio-frequency amplifier of unit 2! is coupled to anantenna system 22, 23. The radio-frequency amplifier of unit 2i includesan adjustable tuning element N which is mechanically connected forunicontrol operation with the adjustable tuning element ii of oscillatorl5, as indicated by the broken line 28.

Considering now the operation of the arrange ment just described, andreferring to the frequency scale of Fig. 2, assume that the carrierwavegenerating system is to operate on any selectable one of a predeterminednumber of transmission channels having equal frequency spacing h. Theoscillator i2 generates oscillations having the frequency 11 and, sincethis frequency is normally relatively low, for example of the order of100 or 200 kilocycles, this oscillator has good absolute frequencystability without requiring that it be of the piezoelectriccrystal-controlled type. If desired, however, the oscillator I! may beof the crystal-controlled type to insure even better frequencystability.

The signal generated by the oscillator i2 thus has a frequency equal tothe frequency spacing between the equally-spaced desired transmissionchannels and this signal is applied to the input circuit of the harmonicgenerator l3. There is derived in the output circuit of generator it amodulation signal having frequency components which may, for example,include the fundamental-frequency component ii of the signal ofoscillator I2 and nine harmonic components fz-fm, inclusive, which areharmonically related to, and preferably, are a continuous band ofharmonics of the signal generated by the oscillator I2, whereby thefrequency components of the modulation signal have relative spacingscorresponding to that of desired transmission channels. This modulationsignal is applied to an input circult of the modulator it and there isapplied to another input circuit of this modulator a carrier wave havinga relatively high and substantially constant frequency in generated bythe oscillator II.

There is consequently derived in the output circuit of the modulator itthe "ontrol carrier wave including a carrier-wave component ofrelatively high and substantially constant frequency and sidebandcomponents of substantially constant frequency and extending over apredetermined frequency band, such components of the control carrierwave having, in the preferred form of the invention, equal spacing inthe frequency spectrum with relation to each other and the frequency ofthe components individually defining predetermined desired transmissionchannels. The term "define" is here used to denote that these componentsindividually so control the oscillator it that the frequency of thecarrier wave generated by oscillator It at any given time corresponds tothat of a selected one of a plurality of transmission channels equal innumber to the components but lying in the frequency spectrum inpredetermined relations with respect to the frequency band of thecomponents, preferably lying above the latter band. The frequencycomponents of this control carrier wave are indicated in Fig. 2 as aspectrum of frequencies shown over the frequency In and extending over afrequency band Ill-fut, the carrierwave component being designated bythe frequency {'11, the lower-sideband components by the frequencies I'mto 1'1, inclusive, and the upper-sideband components by the frequencies)'i to {"m, inclusive.

The control carrier wave is applied from modulator ll to one inputcircuit of the modulator I! while the carrier wav developed by theoscillator I5 is applied to another input circuit of the modulator H.The oscillator I6 is tunable by manual adjustment of the tuning elementit over a predetermined frequency band Ila-I13 which is equal to butdisplaced in the frequency spectrum from the frequency band fiirflfi ofthe control carrier wave, preferably displaced above the latter band,the mean frequency of the band fie-11a being designated as In. Thecarrier wave generated by the oscillator It may thus have any selectablefrequency in this predetermined operatlng frequency band Ila-11a. Thefrequency of the oscillator I0 is so chosen that the carrier wavecomponent In of the. control carrier wave fit-I15 is below and at apredetermined frequency spacing {m from the mean operating frequency inof the oscillator ii. The frequency spacing 11s is preferably chosengreater than one-half of the frequency range fit-{1s of the controlcarrier wave for reasons presently to be explained.

There is thus developed in the output circuit of modulator H in a mannerwell known, an intermediate-frequency control signal having thedifference value of frequency in: whenever the carrier wave ofoscillator l5 has a frequency spaced by the frequency difference fitfrom any of the sideband components fl-fm or f'i-f'uc or thecarrier-wave component )11 of the control carrier wave fld-flS- Thisintermediate-frequency control signal is amplified in the amplifier I 8and applied to the frequency detector id to develop in the outputcircuit thereof a unidirectional control potential the magnitude andpolarity of which vary, as in conventional automatic frequency-controlsystems, with the deviation and sense of deviation of theintermediatefrequency signal from the mean resonant frequency 11a towhich the frequency detector is tuned. This derived unidirectionalcontrol potential is applied to the input circuit of the frequencyshifter 20 so to control the action thereof, as by varying th simulatedreactance of its reactor tube, that the frequency of the oscillator i5is changed in such a direction and to such an extent that the frequencyof the intermediate-frequency control signal is very nearly the value m.This action occurs, of course, each time that the oscillator i5 is sotuned that its frequency is approximately spaced by the frequencyspacing fit from any selected one of th components of the controlcarrier wave. Each time that the frequency of the oscillator I5 is socontrolled, the frequency of the carrier wave generated thereby ismaintained substantially constant on that one of the transmissionchannels which is defined by the fmquency component of the controlcarrier wave that produced the intermediate-frequency control signal.Thus, as the tuning control It or the oscillator II is variedcontinuously in one direction over its operating frequency range fir-ha,the carrier wave generated thereby is stabilized for intervals,depending upon the rate of such tuning, on predetermined transmissionchannels defined by each of the frequency components oi the controlcarrier wave. In using the arrangement of Fig. i, the oscillator i5 ismanually tuned by adjustment of its tuning element It approximately toan operating frequency corresponding to a desired transmission channeland the units l8, l9 and 2B thereupon operate to establish and maintainthe frequency of the oscillator l5 more accurately at the desiredoperating frequency and upon the desired transmission channel which, aspointed out, is defined by one of the frequency components of thecontrol carrier wave I14 to 115.

It will be understood, of course, that the bandpass characteristics ofthe intermediate-frequency amplifier l8 and frequency detector I! aresuch that the automatic-frequency control system comprising units l8, l8and 20 relaxes at least during some portion of the time requiredmanually to tune the oscillator i5 by adjustment of its tuning elementIt from one transmitting channel to an adjacent channel. If this werenot so. the oscillator is could not be tuned from any given channel toevery other channel.

The carrier wave generated by the oscillator I5 is applied to themodulator included in unit H where, after amplitude modulation by thesignal which it is desired to transmit, the modulated-carrier signal isamplified by the radiofrequency amplifier of this unit and applied tothe antenna system 22, 23 for radiation therefrom.

In lieu of the use of an amplitude-modulator stage in unit 2| asdescribed, th signal which it is desired to transmit may alternativelybe applied to the frequency shifter 20 in conventional manner tofrequency-modulate in accordance with such signal the carrier wavegenerated by the oscillator 15.

It has previously been stated that the frequency in of the oscilator IIIis spaced by the frequency difference flfi from the mean operatingfrequenc in of the operating frequency band jlZ-flli of the oscillatorl5 and that the frequency spacing fit is preferably greater than halfthe frequency band fir-fie over which the components of the controlcarrier wave extend. This is desirabie from the standpoint that thereare then no components of the control carrier wave which can beat withthe carrier wave of oscillator i5 to produce image-frequency controlsignals in the output circuit of the modulator ll. While such frequencyspacing of the oscillator i is desirable, it is not essential and thefrequency spacing may be less than one-half of the frequenc rangefii)15. Where this is the case, however, the value of the frequencyspacing fld should be an odd muliiple of one-quarter of the channelspacing defined by the frequency components of the control carrier wave.This insures that any image intermediate-frequenc control signals whichare produced by intermodulation between the carrier wave of oscillator land nonselected components of the control carrier wave have frequenciessufficiently widely spaced from the desired control signal that they arenot translated with appreciable amplitude by the amplifier I! to thedetector trolled oscillator, for generating a plurality of i ll.Whatever small-intensity image signals that are applied to the detectorl'l, however, have frequencies such that the unidirectional controlpotential produced therefrom in the output circuit of the detector i9 socontrols the frequency of the oscillator Ii that the latter is tunedaway from the one of such nonselected components which produces thlargest-intensity image signal and, in being so tuned, is tuned towardthe selected component.

The arrangement of Fig. 1 ha the important advantage that the inputcircuit of the unit 2| is substantially completely decoupled from any ofthe units Ill to I 4, inclusive, and, hence, the control carrier wave issubstantially completely isolated from the input circuit of unit 2|.Consequently, none of the frequency components 01 the control carrierwave can be translated through the unit II to the antenna system 22, 23for radiation therefrom as spurious undesired carrier waves which wouldcause interference with communications carried on with other apparatus.

The band of transmission channels over which a carrier-wave generatingsystem embodying the arrangement of Fig. 1 can be designed to operatedepends, of course, upon the number of harmonic frequencies ofreasonably large amplitude that can be derived b the harmonic generatorit from the oscillations generated by the 0s illator l2. Where thislimited number of transmi sion channels is inadequate for a particularpurpose, the modified form of the invention represented by the schematiccircuit diagram of Fig. 3 is useful. The arrangement of Fig. 3 isessentially similar to that of Fig. 1, similar circuit elements beingdesignated by similar reference numerals and analogous circuit elementsby similar reference numerals primed. The arrangement of Fig, 3 differsfrom that of Fig. l in that it comprises means including at least oneoscillator having means for maintaining the frequency thereofsubstantially constant, preferably at least one piezoelectriccrystal-concarrier waves each including a carrier-wave component ofrelatively high and substantially constant frequencies and sidebandcomponents of substantiall constant frequencies and extending over apredetermined frequency band. The frequencies of the components of eachof such carrier waves individually define predetermined desiredtransmission channels. This means comprises an oscillator Ill having aplurality of piezoelectric crystal devices H, H, H", il', any selectedone of which may be included in circuit with the oscillator ill, bymanual operation of the switch 26. The instant arrangement also includesselector means for selecting a desired one of the components of thecontrol carrier waves, this means comprising a tunable selector 21having an input circuit coupled to the output circuit of the modulatori4 and having an output circuit cou-- pied to the input circuit of themodulator H. The selector 2'! include an adjustable tuning element 28which is connected for unicontrol operation with the adjustable tuninelements It and 24 of the respective units I5 and 21, as indicated bythe broken line 25'. The oscillator ii in this arrangement is tunableover a predetermined operating-frequency band equal to, but displaced inthe frequency spectrum from, the combined frequency bands of the controlcarrier waves developed in the output circuit of the modulator ll.

Considering now the operation of this modified form of the invention,and referring to the frequency scales of Figs. 4 and 5, it may be statedthat, in general, its operation is essentially similar to that of Fig. 1and will not be repeated in detail. There are two alternative manners inwhich the present arrangement may be used to extend the available numberof transmission channels on .which the system may operate. The first ofthese is illustrated in Fig. 4 wherein, for purposes of simplicity, onlytwo control carrier-wave frequency spectra are shown. The carrier-wavecomponent and sideband components of one control carrier wave. forexample, that produced by the oscillator ll under control of thepiezoelectric crystal H, extends over the range fie-fit. while thefrequency of the carrier wave generated by the oscillator Ill undercontrol of another of the crystals, for example the crystal- II, is sochosen that the components of the control carrier wave correspondingthereto extend over a higher frequency Ila-fin, the adjacent endfrequencies lit and he of these two frequency ranges being spaced by thewidth of one transmission channel. The operating frequency band fro-1:1of the oscillator I5 is now equal to the combined frequency band)ll'jlfl of these two control carrier waves, and, actually to thecombined frequency bands of all of the control carrier waves used in thesystem. The frequencies of the crystals II to H', inclusive, areadditionally so chosen that the mid-range of the combined frequency bandof the control carrier waves produced thereby is spaced by a frequencyIn from the mean operating frequency in of the operating frequency bandher-I21 of the oscillator IS. The operation of the Fig. 3 arrangementwhen operated in this manner is otherwise essentiall similar to that ofthe Fig. l arrangement except that the desired component of a givencontrol carrier wave is selected by the selector 21 and applied to themodulator l'l substantially to the exclusive of undesired imagecomponents thereof. The intermediatefrequency control signal developedin the output circuit of the modulator H has a frequency in in thisinstance and the units l8, I9 and 20 operate to establish and maintainsubstantially constant the frequency of the oscillator IS on a selectedone of the transmission channels defined by the control carrier-wavecomponent which is utilized.

An alternative method of operating the Fig. 3 arrangement is illustratedby the frequency scale of Fig. 5. Here the harmonic components of themodulation signal generated by the harmonic generator 13 are more widelysp ced than is the case in the arrangement of Fig. l and define everyfourth desired transmission channel where there are four crystals usedin the oscillator ill. The frequencies of'the crystals II to II'",inclusive. are so chosen with relation to each other that thefrequencies of the components of the control carrier wave produced byeach individually define predetermined desired transmission channels butthe channels defined by a given one of the control carrier waves aredifferent from, and intervene between, at least a portion of thetransmission channels deflnedby at least one other of the controlcarrier waves. The oscillator I! in this case has a frequencycorresponding to the spacing of four desired transmission channels,whereby the frequency spacing of the frequency components of the controlcarrier wave derived by unit H correspondingly define every fourthdesire transmission channel. The frequencies of the crystals I l-l l'"are so chosen with relation to each other that any crystal has afrequency displaced from the next preceding crystal by an amountcorresponding to one desired transmission channel. The control carrierwave developed in the output circuit of modulator H from the carrierwave of the oscillator it under control of the crystal II. for example,is thus as indicated in Fig. 5 by the legend A; that corresponding tothe crystal II by the legend B; that corresponding to the crystal II" bythe legend C: and that corresponding to the crystal II'" by the legendD. It will be seen that the components of the control carrier wave 3 areeach displaced by one desired transmission-channel spacing from thecorresponding component of the control carrier wave A. Similarly, thecomponents of the carrier wave C are displaced from the correspondingcomponents of the carrier wave 18 by one desired transmission-channelspacin and the components of the control carrier wave D are similarlydisplaced from the corresponding components of the control carrier wave0.

In using the arrangement of Fig. 3 and the lastdescribed mode ofoperation, one component of one of the control carrier waves A, B, C orD will define the transmission channel upon which it is desired tooperate. Assuming that this is a component of the control carrier waveC, the switch 26 is adjusted to include the piezoelectric crystal deviceII" in circuit with the oscillator lli' to develop in the output circuitof modulator II the control carrier wave C. The adjustable tuningelement it of the oscillator I5 is then adjusted approximately to thedesired operating frequency and the mechanical connection between theadjustable tuning element It and the adjustable tuning element 28 of theselector 21 causes the latter tuning element simultaneously to beadjusted to condition the selector 21 to select the desired component ofthe control carrier wave C which defines the transmission channel uponwhich it is desired to operate. The selected component of the controlcarrier wave C is applied to one input circuit of modulator I'l todevelop in the output circuit thereof an intermediatefrequency controlsignal having a frequency approximating frequency for. Units i8, i9 and2|) thereupon operate to control the frequency of the oscillator 15, asin the arrangement of Fig. 1, to establish and maintain the frequency ofthe carrler wave generated thereby more exactly on the desiredtransmission channel corresponding to the selected component of thecontrol carrier wave.

It will thus be evident that, by selection of one of the piezoelectricdevices il-I l', inclusive, and suitable adjustment of the tuningelements 24, I6 and 28, the carrier-wave generating system of Fig. 3 maybe caused to operate on any desired transmission channel included in thefrequency band over which the system is designed to operate. In thisrespect, it may be noted that the carrier wave generated by theoscillator l5 may have any selected frequency in a predeterminedfrequency band fro-{'21, this band being equal to but displaced in thefrequency spectrum from the combined frequency bands of the controlcarrier waves A, B, C and D. The operation of this modifled form of theinvention is otherwise essentially similar to Fig. 1 and will not berepeated.

While a tunable selector 21 has been included in the Fig. 3 arrangement,the use of this unit is not essential and the unit may be dispensedwith, if desired, in which case the output circuit of modulator I4 isdirectly connected to one input circuit of the modulator l1. Furthermorea tunable selector similar to unit TI may be included in the arrangementof Fig. 1 between the modulator II and the modulator if. if desired, andwhen so included will operate for the same purpose and in the samemanner as the tunable selector 21 of the Fig. 3 arrangement. A selectorof this nature is primarily useful where the mean frequency of theoperating-frequency band over which the oscillator I! is tunable'isspaced from the frequency of the crystal II in the Fig. 1 arrangement orany of the crystals lli l" in the Fig. 3 arrangement by less thanone-half of the frequency band over which the components of the corn"pending control carrier wave extend. In this event, the tunableselector prevents the application to the modulator I I of suchnon-selected components of a control carrier wave as would produce imageintermediate-frequency control signals in the output circuit of themodulator II.

While it has previously been stated that the sideband components of thecontrol carrier wave preferably have equal spacings in the frequencyspectrum with relation to each other and to the carrier-wave component,it will be evident that only selected ones of the harmonic frequenciesof the modulation signal generated by the harmonic generator I: may beused. In this event, the sideband components of the control carrier wavemay have unequal spacings with relation to each other, but neverthelessdefine desired unequallyspaced transmission channels. An arrangement ofthis nature, is useful, for example, where it is desired to transmit on,say, only the second, fifth, ninth and tenth transmission channels in aband of ten equally-spaced such channels.

From the above description of the invention, it will be apparent that acarrier-wave generating system embodying the invention is adapted togenerate a carrier wave having ahlgh degree of frequency stability and afrequency accurately corresponding to that of any selected one of aplurality of predetermined desired transmission channels. There is thefurther advantage in a system of this nature that there are produced noundesired spurious carrier waves which might cause interference withcommunications carried on by other persons on other channels. Acarrier-wave generating system embodying the invention has theadditional advantage that the frequency of the generated carrier wavemay be and preferably is higher than that of a frequency standard usedin the system. This is particularly important where the frequencystandard comprises a piezoelectric crystal in which case it is desirablefor numerous reasons, for example the lower cost of the crystal, itsruggedness, and the greater ease with which it may be manufactured. thatthe resonant frequency of the crystal be as low as the circumstanceswill permit.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, means for generating a second wave havin any selectablefrequency in a predetermined frequency band equal to but displaced by apredetermined value in the frequency spectrum from said first-namedfrequency band, and means responsive Jointly to the frequency of saidsecand wave and the frequency of that one of said components of saidcarrier wave which is displaced in the frequency spectrum by apredetermined value from the desired operating frequency of said secondwave for maintaining the frequency of said second wave at asubstantially constant desired value.

2. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and. extending over a predeterminedfrequency band, the frequency of said carrier-wave component and thefrequencies of said sideband components being individually related tothe carrier frequencie 01' predetermined desired transmission channels,means for generating a second wave having any selectable frequency in apredetermined frequency band equal to said firstnamed frequency band,and means responsive jointly to the frequency of said second wave andthe frequency of one of said components of said carrier wave formaintaining the frequency of said second wave substantially constant onthe one of said transmission channels related to said one component.

3. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant -frequencies and extending over a predeterminedfrequency band, the frequency spacings of said sideband components withrelation to each other and to said carrier-wave component being equal topredetermined corresponding frequency spacings of desired transmissionchannels whose operating frequencies are related to said components,means for generating a second wave having any selectable frequency in apredetermined frequency band equal to said first-named frequency band,and means responsive jointly to the frequency of said second wave andthe frequency of one of said components for maintaining the frequency ofsaid second wave substantially constant on the one of said transmissionchannels related to said one component.

4. A carrier-wave enerating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, said components of said carrier wave having equalspacings in. the frequency spectrum with relation to each other and thefrequencies of said components being individually related to the carrierfrequencies of predetermined desired transmission channels, means forgenerating a second wave having any selectable frequency in apredetermined frequency band equal to said first-named frequency band,and means responsive Jointly to the frequency of said second wave andthe frequency of one of said components for maintaining the frequency ofsaid second wave substantially constant on the one of said transmissionchannels related to said one component.

5. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, means for generating a second wave having any selectablefrequency in a predetermined frequency band equal to but displaced by apredetermined value higher in the frequency spectrum from saidfirst-named frequency band. and means responsive jointly to thefrequency of said second wave and the frequency of that one of saidcomponents which is displaced in the frequency spectrum by apredetermined value from the desired operating frequency of said secondwave for maintaining the frequency of said second wave at asubstantially constant desired value.

6. A carrier-wave generating system comprising, an oscillator includingmeans for maintaining the frequency thereof substantially constant forgenerating a carrier wav including a carrierwave component of relativelyhigh and substantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, means for generating a second wave having any selectablefrequency in a predetermined frequency band equal to said first-namedfrequency band, and means responsive jointly to the frequency of saidsecond wave and the frequency of that one of said components which isrelated in a predetermined manner to the desired operating frequency ofsaid second wave for maintaining the frequency of said second wave at asubstantially constant desired value.

'7. A carrier-wave generating system comprising, a piezoelectriccrystal-controlled oscillator for generating a carrier wave including acarrier-wave component of relatively high and substantially-constantfrequency and sideband components of substantially constant frequenciesand extending over a predetermined frequency band, means for generatinga second wave having any selectable frequency in a predeterminedfrequency band equal to said first-named frequency band, and meansresponsive jointly to the frequency of said second wave and thefrequency of that one of said components which is related in apredetermined manner to the desired operating frequency of said secondwave for maintaining the frequency of said second wave at asubstantially constant desired value.

8. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, means for generating a second wave having any selectablefrequency in a predetermined frequency band equal to but displaced by apredetermined value in the frequency spectrum from said first-namedfrequency band, means for tuning said second-named generating meansapproximately to a desired operating frequency and for selecting thatone of said carrier-wave components which is displaced in the frequencyspectrum by the said predetermined value from said desired operatingfrequency, and means responsive jointly to the frequency of said secondwave and the frequency of said selected component for establishing andmaintaining the frequency of said second wave more accurately at saiddesired operating frequency.

9. A carrier-wave generating system comprising, means for generating acarrier wave including a carrier-wave component of relatively high andsubstantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, means including an adjustabl tuning element forgenerating a second wave having any selectable frequency in apredetermined frequency band equal to but displaced by a predeterminedvalue in the frequency spectrum from said first-named frequency band,selector means for selecting a desired one of said carrier-wavecomponents, means for operating said adjustable tuning element and saidselector means in unison for tuning said second-named generating meansapproximately to a desired operating frequency and for selecting thatone of said carrier-wave components which is displaced in the frequencyspectrum by the said predetermined value from said desired operatingfrequency, and means responsive jointly to the frequency of said secondwave and the frequency of said selected component for establishing andmaintaining the frequency of said second wave more accurately at saiddesired operating frequency.

10. A carrier-wave generating system comprising, means for generating acarrier wave having a relatively high and substantially constantfrequency, means for generating a modulation signal having frequencycomponents of substantially constant frequencies and predeterminedspacin relative to each other, means for modulating said carrier wavewith said modulation signal to derive a modulated carrier wave includinga carrier-wave component and sideband components extending over apredetermined frequency band. means for generating a second wave havingany selectable frequency in a predetermined frequency band equal to saidfirst-named frequency band. and means responsive jointly to thefrequency of said second wave and the frequency of that one of saidcomponents of said modulated carrier wave which is related in apredetermined manner to the desired operating frequency of said secondwave for maintaining the frequency of said second wave at asubstantially constant desired value.

11. A carrier-wave generating system comprising, means for generating acarrier wave havin a relatively high and substantially constantfrequency, means for generating a modulation signal having frequencycomponents of substantially constant frequencies and having frequencyspacings relative to each other corresponding to the frequency spacingsbetween predetermined desired transmission channels, means formodulating said carrier wave with said modulation signal to derive amodulated carrier wave includin a carrier-wave component and sidebandcomponents extending over a predetermined frequency band and beingindividually related to the carrier frequencies of said predetermineddesired transmission channels, means for generating a second wave havingany selectable frequency in a predetermined frequency band equal to saidfirstnamed frequency band, and means responsive Jointly to the frequencyof said second wave and the frequency of one of said components of saidmodulated carrier wave for maintaining the frequency of said second wavesubstantially constant on the one of said transmission channels relatedto said one component.

12. A carrier-wave generating system comprising, means for generating acarrier wave having a relatively high and substantially constantfrequency, means for generating a modulation signal having frequencycomponents of substantially constant frequencies and having equalfrequency spacings relative to each other and corresponding toequally-spaced predetermined desired transmission channels. means formodulating said carrier wave with said modulation signal to derive amodulated carrier wave including a carrier-wave component and sidebandcomponents extending over a predetermined frequency band and beingindividually related to the carrier frequencies of said predetermineddesired transmission channels, means for generating a second wave havingany selectable frequency in a predetermined frequency band equal to saidfirstnamed frequency band, and means responsive jointly to the frequencyof said second wave and the frequency of one of said components of saidmodulated carrier wave which is displaced in the frequency spectrum by apredetermined selectable value from said first wave for maintaining thefrequency of said second wave substantially constant on theone of saidtransmission channels related to said one component.

13. A carrier-wave generating system comprising, means for generating acarrier wave having a relatively high and substantially constantfrequency, means for generating a signal having a frequency equal to thefrequency spacing between equally-spaced desired transmission channels,means for deriving from said signal a modulation signal having frequencycomponents which are harmonically related to said signal, means formodulatin said carrier wave with said modulation signal to derive amodulated carrier wave including a carrier-wave component and sidebandcomponents extending over a predetermined frequency band and beingindividually related to the carrier frequencies of said desiredtransmission channels, means for generating a second wave having anyselectable frequency in a predetermined frequency band equal to saidfirst-named frequency band, and means responsive Jointly to thefrequency=of said second wave and the fre quency of one of saidcomponents of said modulated carrier wave for maintaining the frequencyof said second wave substantially constant on the one of saidtransmission channels related to said one component.

14. A carrier-wave generating system comprising, means for generating aplurality of carrier waves each including a carrier-wave component ofrelatively high and substantially constant frequency and sidebandcomponents of substantially constant frequencies and extending over apredetermined frequency band, the frequencies of the components of eachof said carrier waves being individually related to the carrierfrequencies of predetermined desired transmission channels and thechannels related to the frequencies of the components of a given one ofsaid carrier waves being different from but intervening between thetransmission channels related to the others of said carrier waves, meansfor generating a second wave having any selectable frequency in apredetermined frequency band equal to the combined frequency bands ofsaid firstnamed carrier waves, and means responsive jointly to thefrequency of said second wave and the frequency of one of saidcomponents for maintaining the frequency of said second wave at asubstantially constant desired value, thereby asoacos to maintain saidsecond wave on the one of said transmission channels related to said onecomponent.

15. A carrier-wave generating system comprising, means for generatingany selectable one of a plurality of carrier waves each including acarrier-wave component of relatively high and substantially constantfrequency and sideband components of substantially constant frequenciesand extending over a predetermined frequency band. the frequencies ofthe components of each of said carrier waves being individually relatedto the carrier frequencies of predetermined desired transmissionchannels and the channels related to a given one of said carrier wavesbeing different from but intervening between the transmission channelsrelated to the others of said carrier waves, means for generating asecond wave having any selectable frequency in a predetermined frequencyband equal to the combined frequency bands of said first-named carrierwaves, and means responsive jointly to the frequency of said second waveand the frequency of one of said components for maintaining thefrequency of said second wave at a substantially constant desired value,thereby to maintain said second wave on the one of said transmissionchannels related to said one component.

16. A carrier-wave generating system comprising, means including atleast one oscillator having means for maintaining the frequency thereofsubstantially constant for generating a plurality of carrier waves eachincluding a carrier-wave component of relatively high and substantiallyconstant frequency and sideband components of substantially constantfrequencies and extending over a predetermined frequency band, thefrequencies of the components of each of said carrier waves beingindividually related to the carrier frequencies of predetermined desiredtransmission channels and the channels related to a given one of saidcarrier waves being different from but intervening between thetransmission channels related to the others of said carrier waves, meansfor generating a second wave having any selectable frequency in apredetermined frequency band equal to the combined frequency bands ofsaid first-named carrier waves, and means responsive jointly to thefrequency of said second wave and the frequency of one of saidcomponents for maintaining the frequency of said second wave at asubstantially constant desired value, thereby to maintain said secondwave on the one of said transmission channels related to said onecomponent.

17. A carrier-wave generating system comprising, piezoelectriccrystal-controlled oscillator means for generating a plurality ofcarrier waves each including a carrier-wave component of relatively highand substantially constant frequency and sideband components ofsubstantially constant frequencies and extending over a predeterminedfrequency band, the frequencies of the components of each of saidcarrier waves being individually related to the carrier frequencies ofpredetermined desired transmission channels and the channels related toa given one of said carrier waves being different from but, interveningbetween the transmission channels related to the others of said carrierwaves, means for generatin a second wave having any selectable frequencyin a predetermined frequency band equal to the combined frequency bandsof said first-named carrier waves, and means responsive jointly to thefrequency of said second wave and the frequency of one or saidcomponents tor maintaining the frequency or substantially maintain saidsecond wave on the transmission channels defined by said one component.

18. A carrier-wave generating system comprisins, means for generatingwaves each of relatively high and quency and sideband components ofsubstantially constant frequencies determined frequency the componentsor each or said carrier waves being individually related or said carrierwaves tervening between at least a portion or the transmission channelssaid carrier and wave having any selectable frequency in a aseaecsquency of said second wave and the frequency one 01' said componentsquency of said second constant desired value, second wave on the one ofnels related to said one component.

19. A carrier-wave genera ins, means tor generating a c in; acarrier-wave componen and substantially constant band components 0quency and extending over a quency band, means for generating a secondwe having any selectable frequency said second wave at a constantdesired value, thereby to one oi said a plurality oi carrier arrier waveinclu including a carrier-wave component substantially constant 1112- 1and extending over a preband. the frequencies or to the carrierfredesired transmission and means responsive jointly being diflerentfrom but inenemy or that one related to at least one other or means forgenerating a sec- 20 waves, second wave for main the frequency siredvalue.

NELSON P. CASE.

Certificate of Correction NELSON P. CASE at errors a pear in the rintedcorrection as follows: age 5, t column, l ne 39, for 8, first column,lines 22 to 24, claim l2 strike out the predetermined selectable e fslpect 1' 5 1 11 i defined by" e 9 t co umn, 1 Q mm or value from Baldfirst wave pa'g '0 should be read with these corrections (1 elated t andthat the said Letters Paton tli ere'sln that the same may conform to therecord of the case in the Patent Office.

of October, A. D. 1946.

Signed and sealed this 15th day Patent No. 2,398,694. April is, 1946.

It is hereby certified th numbered patent requ ring exclusive reademcluston; page words which is displaced m the sirgcification of theabove LESLIE FRAZER for maintaining the frewave at a substantiallythereby to maintain said said transmission chanting system comprist ofrelatively high frequency and sidesubstantially constantfrepredetermined frein a predeterband equal to said first-named thefrequency of said second wave and the fre- 01 said components of saidcarrier wave which is related in a predetermined manner to the desiredoperating frequency or said said second wave at a substantially constantdequency of one or said components tor maintaining the frequency orsubstantially maintain said second wave on the transmission channelsdefined by said one component.

18. A carrier-wave generating system comprisins, means for generatingwaves each of relatively high and quency and sideband components ofsubstantially constant frequencies determined frequency the componentsor each or said carrier waves being individually related or said carrierwaves tervening between at least a portion or the transmission channelssaid carrier and wave having any selectable frequency in a aseaecsquency of said second wave and the frequency one 01' said componentsquency of said second constant desired value, second wave on the one ofnels related to said one component.

19. A carrier-wave genera ins, means tor generating a c in; acarrier-wave componen and substantially constant band components 0quency and extending over a quency band, means for generating a secondwe having any selectable frequency said second wave at a constantdesired value, thereby to one oi said a plurality oi carrier arrier waveinclu including a carrier-wave component substantially constant 1112- 1and extending over a preband. the frequencies or to the carrierfredesired transmission and means responsive jointly being diflerentfrom but inenemy or that one related to at least one other or means forgenerating a sec- 20 waves, second wave for main the frequency siredvalue.

NELSON P. CASE.

Certificate of Correction NELSON P. CASE at errors a pear in the rintedcorrection as follows: age 5, t column, l ne 39, for 8, first column,lines 22 to 24, claim l2 strike out the predetermined selectable e fslpect 1' 5 1 11 i defined by" e 9 t co umn, 1 Q mm or value from Baldfirst wave pa'g '0 should be read with these corrections (1 elated t andthat the said Letters Paton tli ere'sln that the same may conform to therecord of the case in the Patent Office.

of October, A. D. 1946.

Signed and sealed this 15th day Patent No. 2,398,694. April is, 1946.

It is hereby certified th numbered patent requ ring exclusive reademcluston; page words which is displaced m the sirgcification of theabove LESLIE FRAZER for maintaining the frewave at a substantiallythereby to maintain said said transmission chanting system comprist ofrelatively high frequency and sidesubstantially constantfrepredetermined frein a predeterband equal to said first-named thefrequency of said second wave and the fre- 01 said components of saidcarrier wave which is related in a predetermined manner to the desiredoperating frequency or said said second wave at a substantially constantde-

